The invention relates to a method for measuring the specific surface of pulverized materials and apparatus for performing the same.
For pulverized materials being produced and utilized in various industrial branches, the specific surface is one of the characteristic criterions of the production process and the product itself. Previously known methods for measuring this reference value are based either on the determination of the pneumatic resistance of a defined sample bed of a constant volume and mass or on the princple of a light diffraction on individual particles of the measured material.
In the first case the measurement range is limited as the compactibility of the materials being consolidated to the predetermined constant volume by means of vibration or piston compression, depends upon the particle size. For a certain sample volume setting, it is possible to measure the pneumatic resistance only in a rather small range while the measurement accuracy on the upper and lower measurement range limits decreases because of the insufficient homogenity of the sample porosity and the shape of the material sample as well. Even the time interval required for the vibration compression of the sample volume to the predetermined value varies considerably as it depends upon the material fineness. Another undesirable feature of the previously known methods is the dependence of the measuring range upon the mass density of the measured material. Samples of heavy or coarse materials are vibration consolidated to the predetermined volume value in the measuring vessel in a short time but without accomplishing the exact shape, the one being mostly of a cylindrical type. Even when pouring the given sample quantity loosely into the measuring vessel, its upper level was already below the determined volume limit. On the other hand, with very fine materials, the vibration consolidation had to carried out for a very long time which resulted in nonuniformity of the sample porosity; at times one even failed to consolidate the sample to the predetermined volume. When using the other measurement method mentioned above, its accuracy depends upon the material particle shape, and the corresponding measuring equipment is rather complicated and therefore offers lower operational reliability and the respective investment and operational costs are also high.